Implantable radiation therapy device having controllable radiation emission

ABSTRACT

An implantable radiation therapy device includes a biocompatible radiotranslucent outer capsule containing a radiation shielding element and a radioactive isotope at least partially shielded by the shielding element. When the device is at or below body temperature, radiation is prevented or limited from being transmitted through the outer capsule by the shielding element. When non-ambient energy is applied to the device, the shielding element and radioactive isotope are reconfigured such that an increased level of radiation is transmitted through the outer capsule and emitted by the device.

This application is a continuation-in-part of U.S. Ser. No. 09/200,698,filed Nov. 27, 1998, now U.S. Pat. No. 6,066,083 which is herebyincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to implantable radiation therapy devices. Moreparticularly, the invention relates to improved radiation therapy andbrachytherapy devices, also known as radioactive therapeutic seeds, forthe treatment of oncological and other medical conditions.

2. State of the Art

Radioactive seed therapy is a well known and well accepted medicalprocedure for the treatment of various oncological and other medicalconditions. Seed therapy, also known as interstitial brachytherapytypically involves the implantation of one to one hundred relativelysmall capsules (seeds) into or around a treatment site. The capsulescontain a radioactive isotope which irradiates the treatment site atclose range without adversely affecting other parts of the body.Brachytherapy has been used successfully in the treatment of varioustypes of cancers such as prostate cancer. It has also been used toprevent the growth or regrowth of tissues in the treatment of variousocclusive diseases such as arteriosclerosis and arthrosclerosissubsequent to balloon angioplasty.

Radioactive therapeutic seeds are carefully designed to possess severalimportant qualities. First, in the case of prostatic interstitialbrachytherapy they should be relatively small, approximately 0.025 inchin diameter and approximately 0.16 inch long so that they may beimplanted into the prostate gland using minimally invasive instrumentsand techniques. However, it should be appreciated by those skilled inthe art that implantable radioactive sources come in all shapes andsizes. Second, the radioactive isotope must be enclosed in abiocompatible protective package since the seeds are typically notremoved and will remain in the body for many years. Third, each seedpreferably includes a radiopaque (e.g. high Z material) marker so thatit can be located at the treatment site with the aid of fluoroscopy.

The state of the art of radioactive therapeutic seeds is substantiallydisclosed in seven U.S. Patents: U.S. Pat. No. 5,713,828 to Coniglionefor “Hollow-Tube Brachytherapy Device”, U.S. Pat. No. 5,405,309 toCarden, Jr. for “X-Ray Emitting Interstitial Implants”, U.S. Pat. No.4,891,165 to Suthanthiran for “Device and Method for EncapsulatingRadioactive Materials” and U.S. Pat. No. 4,784,116 to Russell, Jr. etal. for “Capsule for Interstitial Implants”, U.S. Pat. No. 4,702,228 toRussell, Jr. et al. for “X-Ray Emitting Interstitial Implants”, U.S.Pat. No. 4,323,055 to Kubiatowicz for “Radioactive Iodine Seed”, andU.S. Pat. No. 3,351,049 to Lawrence for “Therapeutic Metal SeedContaining within a Radioactive Isotope Disposed on a Carrier and Methodof Manufacture”, which are each incorporated by reference herein intheir entireties. In addition, the art has been significantly advancedin co-owned U.S. Ser. Nos. 09/133,072, 09/133,081, and 09/133,082, whichare hereby incorporated by reference herein in their entireties.

The Lawrence patent, which issued in 1967, describes many of theessential features of radioactive therapeutic seeds. Lawrence describesradioactive isotopes (I-125, Pd-103, Cs-131, Xe-133, and Yt-169) whichemit low energy X-rays and which have relatively short half-lives. Whenimplanted at a treatment site, these isotopes provides sufficientradiotherapy without posing a radiation danger to the medicalpractitioner(s), people in the vicinity of the patient, or other partsof the patient's body. Lawrence further describes a protective capsulewhich contains the isotope and prevents it from migrating throughout thebody where it might interfere with healthy tissue. The capsule iscylindrical and made of low atomic number biocompatible materials suchas stainless steel or titanium which do not absorb X-rays. The isotopeis coated on a rod shaped carrier made of similar X-ray transparent(e.g. low Z) material and is placed inside the capsule cylinder which isthen closed. The other patents each provide some improvement over theoriginal Lawrence design.

Despite the fact that radioactive therapeutic seeds have been in use forover thirty years and despite the several significant improvements madein the seeds, many concerns still exist regarding the use of the seeds.One problem is that prior to and during implantation of the therapeuticseeds, the physician must handle the radioactive seeds, and thereforetake precautions to limit his or her exposure. The precautions mayinclude the use of lead lined clothing and limiting the time forcompleting any one procedure. However, such clothing is generally heavyand tiring to wear, and limiting procedure time may not be in the bestinterest of the patient.

In addition, it is difficult to store radioactive therapeutic seeds, asspecial radiation shielding materials must be used in the containerstoring the seeds.

Moreover, there may be situations in which it is desirable to increasethe level of radiation emitted by a seed after implantation, or keep thelevel of radiation at a certain level despite the natural decay of theradioactive source over a more prolonged period of time. For example, itmay be desirable to provide a first dosage of radiation for a period oftime and then, based upon a later diagnosis, increase the dosage for asecond period of time. With the present radioactive implants of the artthis can only be done through a subsequent invasive procedure ofimplanting additional seeds, as radioactive elements decrease theirradiation output according to their respective half-life.

None of the art addresses any manner of providing an “inactive” seedwhich can later, e.g., after implantation, be activated to emitradiation. Likewise, none of the art addresses otherwise increasing theamount of radiation emitted by the seed after the seed is implanted inthe patient, or maintaining a level of radiation over a longer period oftime than the half-life of the radioactive isotope in the implant wouldotherwise permit.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide radioactivetherapeutic seeds which have means for controllably altering theradiation transmitted through the seed capsule.

It is also an object of the invention to provide radioactive therapeuticseeds which are controllably activated to “turn on” the seeds to causeradiation to be emitted therefrom or to increase the radiation emittedtherefrom.

In accord with these objects which will be discussed in detail below,the radioactive brachytherapy seeds of the present invention generallyinclude an outer capsule containing a radioactive material, and asubstantially radiopaque shield which in a first (pre-implantation)configuration substantially obstructs radiation emitted by theradioactive material. One or both of the radioactive material and theshield are controllably movable relative to the other into a second(post-implantation) configuration such that the radioactive material isat least partially unobstructed by the shield. As a result, the level ofradiation emitted by the seed is increased. For purposes herein,“radiopaque” refers to the property of having a relatively “high Z”value, and the terms “radiopaque” and “high Z” are used interchangeablyherein.

Various embodiments of the radioactive material and the radiopaqueshield are provided. In a first embodiment, a low melt temperature low Zmaterial, e.g., wax, includes radioactive particles suspended therein.The low Z material is preferably substantially provided entirely withina high Z casing. The low Z material, with radioactive particles therein,may be heated and forced to flow, by pressurized fluid or mechanicalmeans, through an opening in the high Z casing to at least partiallysurround the high Z casing and substantially cause the seed to emitradiation. In a second embodiment, an elastic or heat shrinkable casingis stretched over a radioactive material and a high Z material isdeposited on the casing. When the radioactive material is heated to amelted state, the force of the casing on the radioactive material movesthe radioactive material out of the casing, the casing collapses, andthe radioactive material surrounds the high Z material on the casing toinitiate or increase radiation emission from the seed. In a thirdembodiment, a flowable radioactive material is retained within aradiopaque casing by a removable barrier. The barrier may be removed bymelting (e.g., a wax stopper barrier), breaking, or by a valvemechanism, and a pressurizing agent then forces the flowable radioactivematerial to surround the radiopaque casing. In a fourth embodiment, afirst member is provided with regions upon which a radioactive isotopeis deposited. The first member is disposed within a second member whichincludes one or more substantially radiopaque regions through whichtransmission of radiation is limited and one more substantiallyradiotransparent regions through which the radiation may be transmitted.In a first configuration, the radiopaque regions are positioned over theradioactive isotope regions. The first member may be controlled to moverelative to the second member, e.g., by heat, vibration, or inertia,into a second configuration wherein the radiotransparent regions arepositioned over the isotope and substantially permit the emission ofradiation by the seed. In a fifth embodiment, a radiopaque shape memoryalloy coil element is provided over an elongate element having anisotope deposited on a portion thereof. The rings of the coil are in anaturally compressed state over the portion of the elongate element onwhich an isotope is provided to prevent transmission of radiationthrough the rings of the coil and out of the outer capsule. The coil istrained to expand when heated and expose the portion of the elongateelement provided with the isotope. In a sixth embodiment, a plurality ofradiopaque shape memory alloy elements are provided, with each elementhaving a portion on which an isotope is deposited. The portions providedwith the isotope are initially oriented inward such that they do notemit radiation through the outer capsule. The elements are trained suchthat when they are heated, the elements change shape (or otherwise move)to substantially expose the portions provided with the isotope andthereby substantially initiate emission of radiation.

It will be appreciated that in embodiments utilizing heat to “activate”the seed, the heat may be provided by hot water, microwave technology,or other radiating means provided at or near (e.g., from adjacent to afew feet away) the seed implant site. Additional means for substantially“activating” or at least increasing seed radioactivity may also be used.

It will be further appreciated that the ability to control the amount ofradiation emitted by the seed enables the physician to “turn on” theseed or at least increase the radiation emitted by the seed whendesired; i.e., upon the application of non-ambient energy, preferably ofa predetermined amount. In addition, the seeds may be relatively safelyhandled without cumbersome precautions prior to activation.

Additional objects and advantages of the invention will become apparentto those skilled in the art upon reference to the detailed descriptiontaken in conjunction with the provided figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view of a first embodiment of an at least partiallyactivatable brachytherapy seed in an “inactive” configuration;

FIG. 1A is a section view of an alternate first embodiment of an atleast partially activatable brachytherapy seed in an “inactive”configuration;

FIG. 2 is a section view of the first embodiment of an at leastpartially activatable brachytherapy seed in an “activated”configuration;

FIGS. 3 and 4 are section views of a second embodiment of an at leastpartially activatable brachytherapy seed in “inactive” and “active” seedconfigurations, respectively;

FIGS. 5 and 6 are section views of a third embodiment of an at leastpartially activatable brachytherapy seed in “inactive” and “active” seedconfigurations, respectively;

FIGS. 7 and 8 are section views of a fourth embodiment of an at leastpartially activatable brachytherapy seed in “inactive” and “active” seedconfigurations, respectively;

FIGS. 9 and 10 are section views of a fifth embodiment of an at leastpartially activatable brachytherapy seed in “inactive” and “active” seedconfigurations, respectively;

FIGS. 11 and 12 are section views of a sixth embodiment of an at leastpartially activatable brachytherapy seed in “inactive” and “active” seedconfigurations, respectively;

FIGS. 13 through 15 are cross section views of the seventh embodiment of“inactive”, “transitional” and “activated” seed configurations,respectively; and

FIGS. 16 through 19 are cross section views of an eighth embodiment ofan at least partially activatable brachytherapy seed in “substantiallyinactive”, “first transitional”, “second transitional”, and “activated”seed configurations, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a radiation therapy seed 10 according to theinvention is shown. The seed 10 includes an inner capsule 12, preferablymade from a radiopaque material, such as lead, provided within abiocompatible outer capsule 14, preferably made from titanium, aluminum,stainless steel, or another substantially radiotranslucent material.Alternatively, referring to FIG. 1A, the inner capsule may be made froma radiotranslucent material and its exterior surface 25 a may be coatedor other provided with, e.g., as a sleeve, a radiopaque material 24 a.Furthermore, while not preferred, the radiopaque material may beprovided to the interior surface 27 a of the inner capsule 12 a (eitherby deposition thereon or an internal sleeve provided thereagainst). Theouter capsule 14 is sealed closed about the inner capsule 12 accordingto any method known in the art, including the methods disclosed inpreviously incorporated U.S. Ser. No. 09/133,081. For treatment of theprostate, the outer capsule preferably has a diameter of less than 0.10inches, and more typically a diameter of less than 0.050 inches, andpreferably has a length of less than 0.50 inches, and more typically alength of less than 0.16 inches.

The inner capsule 12 includes first and second ends 16, 18, andrespective first and second openings 20, 22 at the respective ends. Theinner capsule 12 is preferably coaxially held within the outer capsule14 at the first and second ends 16, 18 of the inner capsule 12, suchthat a preferably uniform space 28 is provided between the inner andouter capsules.

At the first end 16, the inner capsule 12 is at least partially filledwith a meltable solid radioactive material 30. The radioactive materialis preferably a low temperature melting, low Z carrier in whichparticles 31 provided with a radioactive isotope 33 are suspended. Forthe carrier, a low melting point is preferably characterized by under160° F., and more preferably under 140° F. but over 105° F., such thatat room temperature and body temperature, the seed is inactive as theradioactive material is substantially contained within the radiopaqueinner capsule 12. Wax is a preferred carrier, although other carrierssuch as certain metals and polymers may be used. Exemplar isotopesinclude I-125, Pd-103, Cs-131, Xe-133, and Yt-169, which emit low energyX-rays and which a have relatively short half-life.

A piston 32 is provided in the inner capsule 12 and, upon theliquefaction of the radiopaque material 30, is capable of moving, e.g.,by sliding, along a length of the inner capsule. A spring element 34 isprovided between the second end 18 of the inner capsule 12 and thepiston 32, forcing the piston against the radiopaque material.

Turning now to FIG. 2, when it is desired to increase or initiateradiation emission by the seed, that is, “activate” the seed, the seedmay be “activated” by applying heat which causes the radioactivematerial 30 to melt. The heat may be applied, for example, by hot waterprovided in the urethra (for seeds implanted to treat prostaticconditions), by microwave radiation, or by other types of radiation. Thespring element 34 provides force against the piston 32 which, in turn,forces the radioactive material 30 out of the first openings 20 and intothe space 28 between the inner and outer capsules 12, 14. The secondopenings 22 permit gas trapped between the inner and outer capsules 12,14 to be moved into the inner capsule 12 as the radioactive material 30flows and surrounds the radiopaque inner capsule 12. It will also beappreciated that second openings 22 are not required if the space 28 isevacuated during manufacture. Once the radioactive material hassurrounded the inner capsule, the capsule is substantially “activated”.

In a variation of the above, it will be appreciated that someradioactive particles 31 or the isotope 33 may be initially providedoutside the inner capsule (on the exterior surface of inner capsule,interior surface of outer capsule, or within space 28), such thatmovement of the radioactive material 30 out of the inner capsuleoperates to increase, rather than activate, radiation emission by theseed 10.

Referring now to FIG. 3, according to a second embodiment of theinvention, substantially similar to the first embodiment, the radiationtherapy seed 110 includes a radiopaque inner capsule (or inner cylinder)112 provided within a radiotransparent outer capsule 114. The innercapsule 112 includes first and second ends 116, 118, and one or moreopenings 120 at the first end. A solid, low temperature melting,radioactive material 130 is provided within the inner capsule 112.

A piston 132 is provided in the inner capsule 112 against theradioactive material 130, and a pressurized fluid (liquid or gas) 134 isprovided between the piston 132 and the second end 118 of the innercapsule urging the piston toward the first end 116.

Turning now to FIG. 4, the seed 110 may be “activated” by applying heatenergy which causes the radioactive material 130 to melt. Thepressurized fluid 134 then moves the piston 132 away from the second end118, and the piston 132 moves the melted radioactive material 130through the first openings 120 in the inner capsule into the space 128between the inner capsule 112 and the outer capsule 114. Flow of theradioactive material 130 such that the radioactive material surroundsthe inner capsule 112 is thereby facilitated.

Referring now to FIG. 5, according to a third embodiment of theinvention, the radiation therapy seed 210 includes a capsule 214 havingtherein a rod 230 formed from a low melting point radioactive materialwhich is provided with an elastic cover 244, e.g., latex, stretchedthereover. Alternatively, the cover may be made from a heat shrinkablematerial. The cover 244 is provided with a radiopaque coating 226thereon. The rod 230 and cover 244 preferably substantially fill theinterior 246 of the capsule 214. As such, radiation emission is limitedto the ends 248 of the rod.

Turning now to FIG. 6, when the capsule 214 is heated, the rod 230liquefies and the cover 244 collapses inward to force the radioactivematerial out from within the cover. The radioactive material 230 therebysurrounds the collapsed cover 244, with radiopaque material 226deposited thereon, and increases the radioactive emission by the seed210.

Referring now to FIG. 7, according to a fourth embodiment of theinvention, the radiation therapy seed 310 includes an inner capsule 312provided within an outer capsule 314. The inner capsule 312 includesfirst and second ends 316, 318. The first end 316 includes openings 320.A high Z material 326 is deposited on a surface 324 of the inner capsule312. Alternatively, the inner capsule is made from a high Z material.The inner capsule is preferably coaxially held within the outer capsule,and preferably a vacuum is provided therebetween.

The inner capsule 312 is partially filled with a radioactive material330 which is liquid at body temperature, e.g., a dissolved radioactivecompound. The inner capsule is also provided with a pressurized fluid(gas or liquid) 334. A piston 332 separates the radioactive material 330and the pressurized fluid 334. The liquid material 330 is containedwithin the inner capsule by a wax plug 346 or the like, which issubstantially solid at body temperature and which blocks the passage ofthe liquid radioactive material 330 through the openings 320 at thefirst end 316 of the inner capsule 312.

Turning now to FIG. 8, when the seed 310 is heated, the plug 346 ismelted and the pressurized fluid 334 forces the melted plug 346 andradioactive material 330 to exit the openings 320 at the first end 316of the inner capsule 312 and surround the inner capsule and high Zmaterial 326 thereof such that radiation may be emitted by the seed.

It will be appreciated that as an alternative to a wax plug 346 or thelike, a frangible disc or valve may be utilized to retain the liquidradioactive material. The disc or valve may be operated via heat ormechanical means to controllably permit the radioactive material to flowout of the inner capsule.

Referring now to FIG. 9, according to a fifth embodiment of theinvention, the radiation therapy seed 410 includes an inner capsule 412provided within an outer capsule 414. The inner capsule 412 ispreferably held substantially coaxial within the outer capsule by a gaspermeable tube 448, e.g., a mesh or perforate tube formed of a low Zmetal or plastic. The inner capsule 412 is comprised of first and secondpreferably substantially tubular components 450, 452, each having aclosed end 454, 456, respectively, and an open end 458, 460,respectively. The open end 458 of the first component 450 is sized toreceive therein at least the open end 460 and a portion of the secondcomponent 452. The first and second components 450, 452 together therebyform a “closed” inner capsule 412. At least one of the first and secondcomponents is provided with a hole 462 which is blocked by the other ofthe first and second components when the inner capsule is in the“closed” configuration. A gas 434 is provided in the closed innercapsule 412.

The first component and second components 450, 452 are made from asubstantially low Z material. The second component 452 is provided witha plurality of preferably circumferential bands 464 of a radioactivematerial, while the first component 450 is provided with a plurality ofpreferably circumferential bands 466 of a high Z material. The first andsecond components are fit and aligned together such that along thelength of the inner capsule 412 a series of bands in which theradioactive material 464 is covered by the high Z material 466 areprovided. The bands 466 of high Z material substantially block thetransmission of radiation at the isotope bands 464.

Turning now to FIG. 10, when the seed 410 is heated, the gas 434 withinthe inner capsule 412 increases in pressure and forces the secondcomponent axially away from the first component such that the volume ofthe inner capsule increases. As the first and second components 450, 452move axially apart, the hole 462 becomes exposed which equalizes thepressure between the interior of the inner capsule 412 and the interiorof the outer capsule 414, terminating the axial movement. The hole 462is preferably positioned such that movement is terminated with the highZ bands 466 of the first component 450 substantially alternating withthe radioactive isotope bands 464 of the second component 452, such thatthe seed is activated for radiation emission.

It will be appreciated that the other means may be used to move thefirst and second components 450, 452 relative to each other. Forexample, a one-way inertial system or an electromagnetic system may beused. In addition, it will be appreciated that the inner capsule 412 maybe configured such that the high Z bands 466 initially only partiallyblock the radioactive isotope bands 464; i.e., that the seed 410 may beactivated from a first partially activate state to a second state withincreased radioactive emission.

Referring now to FIG. 11, according to a sixth embodiment of theinvention, a radiation therapy seed 610 includes an inner wire 612provided with a circumferential band 676 of radioactive isotopematerial. A close wound shape memory spring coil 678 is positionedcentrally over the inner wire 612 over the band 676 of radioactivematerial. The shape memory coil 678 is preferably made from a relativelyhigh Z material, e.g., Nitinol, and is trained to expand when subject toa predetermined amount of heat. Second and third spring coils 680, 682are positioned on either side of the shape memory coil 678 to maintainthe high Z coil 687 at the desired location. Washers 684 may bepositioned between each of the coils 678, 680, 682 to maintain theseparation of the coils; i.e., to prevent the coils from entangling andto better axially direct their spring forces. The wire 612 and coils678, 680, 682 are provided in an outer capsule 614.

Turning now to FIG. 12, when the seed 610 is subject to a predeterminedamount of heat, the shape memory coil 678 expands to substantiallyexpose the isotope band 676 and to thereby activate the seed.

Referring now to FIG. 13, according to a seventh embodiment of theinvention, a radiation therapy seed 710 includes a relativelyradiotranslucent capsule 714 provided with preferably six rods 786oriented longitudinally in the capsule 714. The rods 786 are made from ashape memory material which preferably is substantially radiopaque,e.g., a nickel titanium alloy. Each end of each rod is provided with atwisted portion 787. In addition, the ends of the rods are secured,e.g., by glue 789 or weld, in the outer capsule 714. When the rods aresubject to heat energy, the rods are adapted to untwist at theirrespective twisted portions 787 about their respective axes. The rods786 are each provided with a longitudinal stripe 788 (preferablyextending about 60° to 120° about the circumference of the rods) of aradioactive isotope along a portion of their length, and preferablyoriented in the capsule 714 such that the stripe 788 of each is directedradially inward toward the center C of the capsule with the high Zmaterial of the rod substantially preventing or limiting transmission ofradiation therethrough.

Turning now to FIG. 14, when subject to heat energy, the shape memoryrods 786 within the seed 710 twist (or rotate) along their axes. Therods 786 are preferably oriented such that adjacent rods rotate inopposite directions. Turning now to FIG. 15, the rods 786 are trained torotate preferably 180° about their respective axes. As a result, theisotope stripe 788 along each of the rods 786 is eventually directedradially outward to activate radiation emission by the seed.

It will be appreciated that the rods 786 are not required to besubstantially radiopaque and that alternatively, or additionally, therods may be circumferentially deposited with a relatively high Zmaterial along their length at least diametrically opposite thelongitudinal stripes of radioactive isotopes, and preferably at alllocations on the rods other than on the stripes 788. Furthermore, itwill be appreciated that fewer than six or more than six rods may beprovided in the capsule. Moreover, a central rod may also be used tomaintain the rods in the desired spaced apart configuration; i.e., suchthat the rods together form a generally circular cross section.

Referring now to FIG. 16, according to an eighth embodiment of theinvention, a radiation therapy seed 810 includes a relativelyradiotranslucent capsule 814 provided with preferably three elongateshape memory strips 890 positioned lengthwise in the capsule 814. Itwill be appreciated that two or four or more strips 890 may also beused. The strips are preferably made from Nitinol and are alsopreferably coated with a high Z material 891, e.g., gold or a heavymetal, on one side (an initially outer side), and with a radioactiveisotope 892 on the side opposite the high Z material (an initially innerside). The strips 890 are preferably positioned in the capsule at 120°relative separation. The configuration of the strips 890 and the high Zmaterial on the outer side of the strips substantially limits radiationemission by the seed, as radiation is emitted only from between the endsof the strips, at 896.

The shape memory strips 890 are trained to bend. As shown in FIGS. 17through 19, when heat is applied to the seed, the strips 890 fold intotheir bent configuration such that eventually the radioactive material892 of the strips 890 is located substantially on an exterior surface ofthe strips, while the high Z material is located on an interior side ofthe strips to further activate the seed. The strips 890 may be coupledto the capsule 814 by posts (not shown) to maintain their relativepositions during bending.

There have been described and illustrated herein several embodiments ofan activatable radioactive therapeutic seed. While particularembodiments of the invention have been described, it is not intendedthat the invention be limited thereto, as it is intended that theinvention be as broad in scope as the art will allow and that thespecification be read likewise. For example, those skilled in the artwill appreciate that certain features of one embodiment may be combinedwith features of another embodiment to provide yet additionalembodiments. Also, while hot water is disclosed as a heat source for“activating” many of the embodiments of the “activatable” seeds, it willbe appreciated that microwave technology or other forms of radiatedenergy transmitted from a distance or provided at or near the seedimplant site may also be used to generate sufficient heat. In addition,while a particular preferred temperature range for melting theradioisotope carrier is disclosed, it will be appreciated that a carriermay be used which melts at any temperature at or between bodytemperature, i.e., approximately 98° F., and an upper temperature whichwill not cause severe damage to body tissue if applied for a very shortperiod of time, i.e., approximately 212° F. Thus, for example, seedswhich are intended to be activated at body temperature are preferablystored at room temperature or kept refrigerated prior to use, but maynot be handled by the practitioner without substantial activation.Furthermore, it will be appreciated that other types of energy can beused to trigger partial or complete seed “activation”. For example,mechanical, electromagnetic, and piezoelectric energy can also be used.In addition, while particular dimensions have been disclosed for theseeds, it will be appreciated that other dimensions may be likewise beused depending on the particular application of the seed; i.e., itslocus of implantation. Also, it will be appreciated that the terms“radiotransparent”, “radiotranslucent”, “radiolucent”, and “low Z” areintended to have the same meaning for purpose of the prior descriptionand in the construction of the claims which follow. In addition, theabove “activatable” embodiments in conjunction with the “deactivatable”embodiments of the previously incorporated parent case, provide acomplete system in which the radiation transmission of a brachytherapyseed can be controllably altered. It will therefore be appreciated bythose skilled in the art that yet other modifications could be made tothe provided invention without deviating from its spirit and scope as soclaimed.

What is claimed is:
 1. An implantable radiation therapy device,comprising: a) a biocompatible outer capsule having a wall adapted totransmit radiation therethrough; b) a radioactive material locatedinside said outer capsule and emitting radiation; and c) control meansinside said capsule for controllably altering an amount of saidradiation transmitted through said outer capsule, wherein saidradioactive material and said control means are irremovable from insidesaid capsule without opening said capsule.
 2. An implantable radiationtherapy device according to claim 1, wherein: said control meansoperates to increase the amount of radiation transmitted through saidouter capsule.
 3. An implantable radiation therapy device according toclaim 1, wherein: said control means includes a radiopaque shieldmovable between first and second configurations, wherein in said firstconfiguration said radiopaque shield prevents a first amount of saidradiation from reaching said outer capsule, and in said secondconfiguration said radiopaque shield permits a greater amount of saidradiation from reaching said outer capsule.
 4. An implantable radiationtherapy device according to claim 1, wherein: said control meansincludes a shape memory alloy.
 5. An implantable radiation therapydevice according to claim 1, wherein: said control means includes one ofa spring and a pressurized fluid.
 6. An implantable radiation therapydevice according to claim 1, wherein: said control means includes acollapsible sleeve.
 7. An implantable radiation therapy device accordingto claim 1, wherein: said radioactive material includes a carrier withradioactive elements suspended therein.
 8. An implantable radiationtherapy device according to claim 7, wherein: said carrier melts at atemperature between body temperature and a relatively higher temperaturewhich does not exceed a temperature will cause severe damage to bodytissue.
 9. An implantable radiation therapy device according to claim 1,wherein: said radioactive material is liquid at body temperature.
 10. Aradiation therapy device implantable within a human body, comprising: a)a biocompatible outer capsule having a wall adapted to transmitradiation therethrough; b) a radioactive material located inside saidouter capsule; and c) a radiopaque shield located inside said outercapsule, wherein when said device is in a first state, said radiopaqueshield and said radioactive material are configured to allow a firstamount of radiation transmission through said outer capsule, and whereinupon application of non-ambient energy to said device, said deviceenters into a second state in which said radioactive material and saidradiopaque shield are otherwise configured to permit a second amount ofradiation transmission through said outer capsule, said second amountbeing different than said first amount, wherein when said device isimplanted in the human body, said non-ambient energy is appliablewithout physical contact between said device and an instrumentcontrollable from outside the human body.
 11. An implantable radiationtherapy device according to claim 10, wherein: said first amount issubstantially zero.
 12. An implantable radiation therapy deviceaccording to claim 10, wherein: said second amount is greater than saidfirst amount.
 13. An implantable radiation therapy device according toclaim 10, wherein: in said first state, said radiopaque shieldsubstantially surrounds said radioactive material.
 14. An implantableradiation therapy device according to claim 10, further comprising: d)an inner capsule provided in said outer capsule, said inner capsulebeing made of a radiopaque material, and including at least one openingand defining an interior, wherein in said first state, said radioactivematerial is substantially provided in said interior of said innercapsule, and in said second state said radioactive material is at leastpartially located outside said interior of said inner capsule.
 15. Animplantable radiation therapy device according to claim 14, wherein:said inner capsule is held coaxial in said outer capsule.
 16. Animplantable radiation therapy device according to claim 14, wherein:said radioactive material includes a carrier having radioactive elementssuspended therein.
 17. An implantable radiation therapy device accordingto claim 14, wherein: said radioactive material is in a liquid state atbody temperature, and said radiation therapy seed further comprises, e)a means for preventing said radiopaque material from flowing throughsaid at least one opening when said seed is in said first state.
 18. Animplantable radiation therapy device according to claim 17, wherein:said means for preventing comprises a meltable plug which melts uponapplication of said non-ambient energy.
 19. An implantable radiationtherapy device according to claim 16, wherein: said carrier melts at atemperature between body temperature and a relatively higher temperaturewhich does not exceed a temperature will cause severe damage to bodytissue.
 20. An implantable radiation therapy device according to claim19, wherein: said carrier is one of liquid, wax, a polymer, and metal.21. An implantable radiation therapy device according to claim 16,further comprising: e) means for moving said carrier from said interiorthrough said at least one opening in said inner capsule, and into aspace between said inner capsule and said outer capsule.
 22. Animplantable radiation therapy device according to claim 21, wherein:said means for moving is one of a spring element and a pressurizedfluid.
 23. An implantable radiation therapy device according to claim10, wherein: said radioactive material is liquid at body temperature.24. An implantable radiation therapy device according to claim 10,further comprising: a covering over said radioactive material, saidcovering having a surface on which said radiopaque shield is provided,said radioactive material adapted to melt upon application of saidnon-ambient energy, and said covering is at least one of elastic andheat-shrinkable, such that when said non-ambient energy is applied tosaid seed, said radioactive material melts and said covering contractsforcing said melted radioactive material from said cover to at leastpartially surround said radiopaque material.
 25. A radiation therapydevice implantable within a human body, comprising: a) an implantablecontainer having a wall adapted for the transmission of radiationtherethrough; b) a radioactive isotope which emits radiation and whichis provided in said container; and c) a movable shield provided in saidcontainer for increasing the radiation transmitted through saidcontainer relative to the radiation emitted by said isotope when anamount of energy is applied to said device, wherein when said device isimplanted in the human body, said amount of energy is appliable withoutphysical contact between said device and an instrument controllable fromoutside the human body.
 26. An implantable radiation therapy deviceaccording to claim 25, wherein: said amount of energy is heat at atemperature above body temperature.
 27. An implantable radiation therapydevice according to claim 25, further comprising: d) a member having aportion upon which said isotope is provided, wherein said shield is asubstantially radiopaque shape memory metal extended over and coveringsaid member, and adapted to move and expose said portion of said memberon which said isotope is provided when said energy is applied to saidshaped memory metal.
 28. An implantable radiation therapy deviceaccording to claim 25, wherein: said shield comprises a substantiallyradiopaque portion on a plurality of shape memory members, each alsohaving a portion upon which said isotope is provided, said plurality ofmembers arranged in said container such that said portion having saidisotope is substantially prevented from emitting radiation through saidcontainer without substantial interference from said substantiallyradiopaque portions, wherein said shape memory members include apredisposition to at least one of bend, rotate and twist uponapplication of said amount of energy such that said portions upon whichsaid isotope is provided at least partially surround said radiopaqueportions.
 29. An implantable radiation therapy device according to claim28, wherein: said shape memory members are each in the form of anelongate rod and comprised of a substantially radiopaque material, andsaid isotope is provided along a longitudinal portion of each said shapememory member.
 30. An implantable radiation therapy device according toclaim 28, wherein: said shape memory members are each in the form oflongitudinal strip having first and second sides, each being predisposedto bend along a longitudinal axis over said first side, said first sidebeing provided with a substantially radiopaque material and said secondside being provided with said radioactive isotope, wherein uponapplication of said amount of energy said members at least partiallybend about said longitudinal axis such that said portions on which saidisotope is provided are substantially exposed and unshielded by saidradiopaque material.
 31. A radiation therapy device implantable within ahuman body, comprising: a) an implantable container having a walladapted for the transmission of radiation therethrough; b) a radioactiveisotope which emits radiation and which is provided in said container;and c) a movable element provided in said container which moves when anamount of energy is applied to said device, wherein when said device isimplanted in the human body, said amount of energy is appliable withoutphysical contact between said device and an instrument controllable fromoutside the human body.
 32. An implantable radiation therapy deviceaccording to claim 31, wherein: said movable element includes aradiopaque portion.
 33. An implantable radiation therapy deviceaccording to claim 31, wherein: said movable element includes saidradioactive isotope.
 34. An implantable radiation therapy device,comprising: a) a biocompatible outer capsule having a wall adapted totransmit radiation therethrough; b) a radioactive material locatedinside said outer capsule and emitting radiation; and c) control meansfor controllably altering an amount of said radiation transmittedthrough said outer capsule, said control means including a collapsiblesleeve.
 35. An implantable radiation therapy device, comprising: a) abiocompatible outer capsule having a wall adapted to transmit radiationtherethrough; b) a radioactive material located inside said outercapsule and emitting radiation, said radioactive material including acarrier with radioactive elements suspended therein and said carriermelting at a temperature between body temperature and a relativelyhigher temperature which does not exceed a temperature will cause severedamage to body tissue; and c) control means for controllably altering anamount of said radiation transmitted through said outer capsule.
 36. Animplantable radiation therapy device, comprising: a) a biocompatibleouter capsule having a wall adapted to transmit radiation therethrough;b) a radioactive material located inside said outer capsule and emittingradiation, said radioactive material being in a liquid state at bodytemperature; and c) control means for controllably altering an amount ofsaid radiation transmitted through said outer capsule.
 37. Animplantable radiation therapy device, comprising: a) a biocompatibleouter capsule having a wall adapted to transmit radiation therethrough;b) a radioactive material located inside said outer capsule; c) aradiopaque shield located inside said outer capsule; and d) an innercapsule provided in said outer capsule, said inner capsule being made ofa radiopaque material, and including at least one opening and definingan interior, wherein when said device is in a first state, saidradiopaque shield and said radioactive material are configured to allowa first amount of radiation transmission through said outer capsule,said radioactive material being substantially provided in said interiorof said inner capsule, and wherein upon application of non-ambientenergy to said device, said device enters into a second state in whichsaid radioactive material and said radiopaque shield are otherwiseconfigured such that said radioactive material is at least partiallylocated outside said interior of said inner capsule to permit a secondamount of radiation transmission through said outer capsule, said secondamount being different than said first amount.
 38. An implantableradiation therapy device, comprising: a) a biocompatible outer capsulehaving a wall adapted to transmit radiation therethrough; b) aradioactive material located inside said outer capsule, said radioactivematerial being in a liquid state at body temperature; and c) aradiopaque shield located inside said outer capsule, wherein when saiddevice is in a first state, said radiopaque shield and said radioactivematerial are configured to allow a first amount of radiationtransmission through said outer capsule, and wherein upon application ofnon-ambient energy to said device, said device enters into a secondstate in which said radioactive material and said radiopaque shield areotherwise configured to permit a second amount of radiation transmissionthrough said outer capsule, said second amount being different than saidfirst amount.
 39. An implantable radiation therapy device, comprising:a) a biocompatible outer capsule having a wall adapted to transmitradiation therethrough; b) a radioactive material located inside saidouter capsule; c) a radiopaque shield located inside said outer capsule;and d) a covering over said radioactive material, said covering having asurface on which said radiopaque shield is provided, wherein when saiddevice is in a first state, said radiopaque shield and said radioactivematerial are configured to allow a first amount of radiationtransmission through said outer capsule, and wherein said radioactivematerial adapted to melt upon application of said non-ambient energy,and said covering is at least one of elastic and heat-shrinkable, suchthat when said non-ambient energy is applied to said seed, saidradioactive material melts and said covering contracts forcing saidmelted radioactive material from said cover to at least partiallysurround said radiopaque material so that said device enters into asecond state in which a second amount of radiation transmission ispermitted through said outer capsule, said second amount being differentthan said first amount.
 40. An implantable radiation therapy device,comprising: a) a container having a wall adapted for the transmission ofradiation therethrough; b) a radioactive isotope which emits radiationand which is provided in said container; and c) a movable shieldprovided in said container for increasing the radiation transmittedthrough said container relative to the radiation emitted by said isotopewhen heat at a temperature above body temperature applied to saiddevice.
 41. An implantable radiation therapy device, comprising: a) acontainer having a wall adapted for the transmission of radiationtherethrough; b) a radioactive isotope which emits radiation and whichis provided in said container; c) a member having a portion upon whichsaid isotope is provided; and d) a movable shield provided in saidcontainer for increasing the radiation transmitted through saidcontainer relative to the radiation emitted by said isotope when anamount of energy is applied to said device, wherein said shield is asubstantially radiopaque shape memory metal extended over and coveringsaid member, and adapted to move and expose said portion of said memberon which said isotope is provided when said energy is applied to saidshaped memory metal.
 42. An implantable radiation therapy device,comprising: a) a container having a wall adapted for the transmission ofradiation therethrough; b) a radioactive isotope which emits radiationand which is provided in said container; and c) a movable shieldprovided in said container for increasing the radiation transmittedthrough said container relative to the radiation emitted by said isotopewhen an amount of energy is applied to said device, said shieldcomprising a substantially radiopaque portion on a plurality of shapememory members, each also having a portion upon which said isotope isprovided, said plurality of members arranged in said container such thatsaid portion having said isotope is substantially prevented fromemitting radiation through said container without substantialinterference from said substantially radiopaque portions, wherein saidshape memory members include a predisposition to at least one of bend,rotate and twist upon application of said amount of energy such thatsaid portions upon which said isotope is provided at least partiallysurround said radiopaque portions.
 43. An implantable radiation therapydevice, comprising: a) a container having a wall adapted for thetransmission of radiation therethrough; b) a movable element provided insaid container which moves when an amount of energy is applied to saidseed, c) a radioactive isotope which emits radiation, said movableelement including said radioactive isotope.